Sequence of Events During Peptide Unbinding from RNase S: A Complete Experimental Description

TL;DR

This study uses transient IR spectroscopy to detail the sequence of peptide unbinding from RNase S, revealing unfolding, unbinding, and protein response timescales, and clarifying the binding mechanism.

Contribution

It provides a comprehensive experimental timeline of peptide unbinding from RNase S, combining light-triggered disruption with multi-scale spectroscopic observation.

Findings

Peptide unfolds within 20 ns in the binding pocket.

Unbinding occurs after approximately 300 microseconds.

Protein structural response is observed after 3 ms.

Abstract

The photo-triggered unbinding of the intrinsically disordered S-peptide from the RNase S complex is studied with the help of transient IR spectroscopy, covering a wide range of time scales from 100 ps to 10 ms. To that end, an azobenzene moiety has been linked to the S-peptide in a way that its helicity is disrupted by light, thereby initiating its complete unbinding. The full sequence of events is observed, starting from unfolding of the helical structure of the S-peptide on a 20 ns timescale while still being in the binding pocket of the S-protein, S-peptide unbinding after 300 microseconds, and the structural response of the S-protein after 3 ms. With regard to the S-peptide dynamics, the binding mechanism can be classified as an induced fit, while the structural response of the S-protein is better described as conformational selection.